1. Field of the Invention
This invention relates to an optical recording medium which is suitable for writing recording with laser beam, particularly semiconductor laser beam, more particularly to an optical recording medium which can be used for optical disc or optical card technique.
2. Related Background Art
Generally speaking, an optical recording medium such as optical disc or optical card can record information at a high density by forming small pits of, for example, about 1 .mu.m which can be optically detected on a thin recording layer provided on a substrate having spiral, circular, linear grooves, etc.
When the laser beam converged on the surface of the recording layer is scanned, the recording layer absorbs the laser energy to form optically detectable pits, whereby information is written.
For example, according to the heat mode recording system, the recording layer absorbs heat energy and can form small concave pits by evaporation or melting at that site. According to another heat mode recording system, by absorption of the laser energy irradiated, pits having optically detectable density difference can be formed at that site.
As the optical recording medium to be used for this kind of optical recording and reproducing device, there has been known one constituted of a substrate, a metal reflective layer and a recording layer containing a dye. This optical recording medium is formed so that the laser beam incident on the recording layer containing a dye may reach the metal reflective layer and the reflected light reflected thereagainst can be easily detected, and in this case, the metal reflective layer is provided for supplementing the amount of reflected light which is defficient with only the recording layer.
However, presence of the metal reflective layer makes the constitution of the optical recording medium complicated, and is also a cause for high cost.
In contrast, the above problems can be solved by use of an organic dye thin film as the recording layer with high reflectance.
Particularly, when an azulene type dye disclosed in U.S. Pat. No. 4,548,886 is used as one having great light absorption relative to laser beam, a light absorptive reflective film exhibiting metallic luster (reflectance: 10-50%) can be obtained, whereby an optical recording medium capable of laser recording and also capable of reflective reading can be obtained.
Particularly, when a semiconductor laser with oscillation wavelength of 700 to 800 nm is used as a laser light source, miniaturization and reduction in cost of the device is rendered possible.